The key roller of the conventional instrument is constituted as shown in FIG. 8, and therefore, there exist the following difficulties. That is, the determination of the gap between a roller 5' and a roller connector 7' is difficult when assembling. Further, during the use of the instrument, the sliding portion for the roller 5' and a roller shaft 10' wear out, thereby forming a gap between the roller 5' and the roller connector 7' making. Further, during musical performances, the thread portion 11' becomes loosens, and therefore, the roller shaft 10' and the roller connector 7' are liable to become detached from each other. Further, once the roller is worn out, re-adjustment is impossible, thereby requiring replacement of the roller itself, which is an uneconomical feature of the conventional roller.